In the manufacture of clothing it is often necessary to feed small sections or pieces of fabric into processing machines which edge, sew, and the like. For example, in making dungarees or, jeans, the rear seat patch pockets will first be cut as rectangles or polygons of denim, and then singly fed to a machine for hemming the top edge (prior to sewing the patch onto the pants to form the pocket). Or, one leg piece will be fed to a machine for sewing on a fly zipper tape.
Typically fabric pieces will be simultaneously cut from multiple layers, and arrive at the processing machine stacked. The stacks of fabric pieces may have individual pieces variously turned face up or face down; jeans fabric, for example, usually has a dark side and a light side, and the pieces must be fed into the hemming machine with the proper side up if the jeans are to be assembled correctly.
In the manufacture of jeans, pieces like pocket patches and fly material have traditionally been picked off from a stack manually and hand fed into the sewing or processing machine, because existing devices were unable to reliably perform the necessary operations, which are: first, picking up from the stack only the single top piece of fabric (to avoid feeding double pieces to the processing machinery); next, inspecting the pieces to determine whether the dark or light side is facing up; third, flipping those pieces which are wrongly oriented; and the fourth, feeding the individual pieces into the processing machine.
The prior art shows numerous devices for picking up layers or sheets of material from a stack. Many of these devices are designed for picking relatively stiff or inflexible materials like sheet metal or paper, and they cannot be used to pick cloth, which crumples easily, when compression forces parallel to its surface are used. Other devices known in the prior art, which use vacuum or air jets, are unsuited to picking up fabric because it is permeable to air flow.
The Bernoulli effect can be used to pick up a sheet of paper. This is disclosed by Zimmerman et al. in U.S. Pat. No. 4,763,890. Air is expelled from a linear array of nozzles across the surface of the top sheet in a stack. Reduced pressure resulting from the air velocity across the upper surface of the paper lifts the edge of the top sheet, which is then grasped by mechanical jaws. This technique, as disclosed by Zimmerman, may not work well with cloth due to the greater surface roughness which is a characteristic of cloth and may slow the sheet of air, the permeability of cloth which will lessen the pressure difference across the top sheet by air leakage, and also by cloth's tendency to flap which would make grasping by the jaws erratic.
Suction cups are widely used for picking up sheets of paper in printing presses and other devices. A suction cup is defined in the present specification, and in the following claims, as a hollow article having a lip for contacting a surface and for at least partially sealing against fluid leakage between the lip and the contacted surface. Suction or a partial vacuum inside the hollow of the cup causes ambient air pressure to force the cup against the contacted surface and so hold it by friction against the lip. Suction cups may have a closed hollow end, as in a child's rubber-tipped arrow, or may have their hollow ends connected to a vacuum source to supply suction. The latter type of suction cup is used in more machinery. Often the vacuum is valved for control of the suction force. Suction cups are almost always of resilient or rubbery material, both because this allows the lip to conform to surface irregularities and because the high coefficient of friction aids in picking up the sheet.
While suction cups are very useful for picking up sheets which are impermeable (e.g., sheet metal) or only somewhat porous (e.g., paper), they are generally ill-suited to removing stacked permeable sheets such as cloth or fabric workpieces, because of air leakage through the fabric. As a suction cup, with a partial vacuum in the cup, comes into contact with and covers the top sheet of a piece of fabric in a stack, air rushes through the permeable material of the top sheet; this air must also flow up through the adjacent sheet, second down in the stack, on its way to the topmost first sheet. The air flow through the resisting weave of the second sheet creates a pressure difference, and a force, which may pick up the second sheet as well as the top sheet.
The prior art does not show a suitable arrangement of suction cups for use in picking the single top sheet from a stack of permeable sheets.
Schwebel, in U.S. Pat. No. 3,937,457, teaches the use of suction cups axially mounted on the ends of swinging arms. His invention is intended to automatically align and/or stretch sheets as they are picked up from a stack. The arms are gimballed in two perpendicular directions, so that the suction cups are capable of ganged swinging in narrow arcs both in the direction of feed and also across it. The motion is limited by stops to narrow angles only. The arms are held in neutral positions by springs, and rock through their arcs as a result of friction between the suction cup lips and the top sheet. Schwebel discloses no active means of swinging the arms. The object of the Schwebel invention is to stretch a sheet, which would most likely result in wrinkles with most cloth or fabric.
U.S. Pat. No. 4,759,537, issued to Illig et al., shows a "suction pickup device" having a stem extending axially from a vacuum pipe. The stem terminates distal the vacuum pipe in a lip surrounding a hollow space connected to the vacuum pipe. The lip lies in a plane which is inclined to the common axis of the vacuum pipe and stem. The vacuum pipe moves axially toward and away from the surface of the top sheet of the stack for picking off sheets. The sheet stack top surface is inclined to the vacuum pipe/stem axis at the same angle as the lip plane is, so that the lip plane is always parallel to the stack surface, and the lip will lie flat on the top sheet when the pipe is extended to bring the lip and the top surface into contact. A vacuum is applied through the pipe and stem to hold the top sheet when contact is made.
The resilience of the stem is not discussed by Illig et al. The cross-hatching in his drawing indicates that the stem is made of resin or plastic material, but not of rubber or electrical insulation. Due to the fixed parallel orientation of the pipe/stem axis to the top sheet, the stem need not be resilient, or need be only minimally resilient.
Hoenigmann, in U.S. Pat. No. 4,002,332, shows a suction cup hingedly mounted at the end of a vacuum pipe for lifting metal sheets from a stack. The vacuum pipe and cup are moved, by a mechanism with perpendicular tracks attached to a frame, for lifting sheets from the top of the stack and feeding them into a machine. Unlike the Illig et al. invention, in which the entire arm pivots with the cup rigidly attached at the end, Hoenigmann's arm-like vacuum pipe member is non-rotating; the cup alone pivots. The pivot is apparently needed because the metal sheets will curve under their own weight and would break the seal without it. It appears that this pivot would not be needed to pick flexible cloth, which is easily held to the perimeter of a suction cup lip.
The prior art also shows devices for flipping over a sheet of material, but none of these is seen as being suitable for flipping a piece of fabric, such as denim.
The majority of disclosed flipping devices employ complex arrangements of parallel rollers, like those of printing presses. These flip a sheet by bending it in one dimension. See, for example, U.S. Pat. Nos. 4,346,880, 4,968,021, and 5,106,075. Such flippers are ill-suited to inverting cloth, which will bunch and jam in the rollers unless special tension means are employed to prevent it, as in a tape recorder drive. Also, any roller must reverse the direction of a sheet while inverting it, making roller devices ill-suited to flipping sheets travelling along a linear path.
U.S. Pat. No. 3,622,151, issued to Range, describes one device for linear-path flipping. His "fluidic flipover" apparatus for letter envelopes comprises a long and rather thin hollow box, which is twisted about its longest center line through an angle of 180 degrees. The interior of the box is pressurized with air. One side of the box, which is the envelope transport surface, is drilled with numerous air jet holes. The air holes are angled in the direction of transport. An envelope placed against the side of the box at one end is blown along the length of the box to the other end by the angled air jets.
The air jets levitate the letter near the surface for low friction. Air from the jets under the envelope must escape and flow outward from the letter perimeter: this means higher air velocity between the envelope and the box than between the envelope and the atmosphere, and so lower pressure by the Bernoulli effect. The higher atmospheric pressure holds the envelope onto the box surface.
As the envelope travels along the twisted transport surface it is likewise twisted through 180 degrees, and arrives at the far end of the box inverted.
The Range fluidic flipover is seen to be unsuitable for fabrics, because the force on the trailing edge of a piece of fabric will be greater than the force on the front edge. (The air jet impinges against the trailing edge but not the front edge.) Without paper's stiffness, the cloth would bunch, lose contact area, and blow off the track.
In sum, the prior art does not disclose any device or method for picking the top sheet from a stack of air-permeable, flexible sheets that is simple and inexpensive to implement, uses available parts, and is reliable. Neither is there disclosed a simple device for flipping flexible sheets transported linearly; nor is the prior art seen to teach any combination of devices suitable for picking and flipping fabric.